1. Field of the Invention
The present invention relates generally to vibrating screen separators for processing commingled mixtures and separating and assorting their solid constituents. More particularly, the present invention relates to separator screen machines, and to methods and apparatus for adjustably tensioning the vibrating screens they use for sifting and separating aggregates.
2. Description of the Related Art
Numerous screen separator devices are known in the art for processing commingled mixtures. With machinery of this nature, aggregates of various desired sizes are separated from differently sized portions of an incoming raw mixture. Typical separator devices are associated with suitable bulk handling equipment, including chutes, conveyors and the like, that deliver raw material to the separator, and thereafter transfer separated constituent elements away from the separator stages for further processing or storage or shipment. Screen separators designs involve multiple generally planar, screens that are mounted on subframes and vibrated during operation. Screens or groups of screens may be stacked vertically, or arranged serially in a processing plant. Elements of materials traversing the vibrating screens gravitationally drop below for further collection and processing. Numerous successive screening steps are often accomplished with laterally adjacent or vertically stacked screen decks. Typically the separator screens are tightly mounted and supported within an encircling subframe that is secured to the machine framework. Vigorous agitation in the form of screen vibration and/or oscillation is imparted through a variety of different mechanical systems causes material movement and enhances the separation effects.
Prior art vibrating screen separators are seen in prior U.S. Pat. No. 4,274,953, issued Jun. 23, 1981, and U.S. Pat. No. 5,199,574 issued Apr. 6, 1993, both of which are entitled “Vibrating Screen Separator.” Both of these patents are assigned to J & H Equipment, Inc., the instant assignee. The latter reference discloses a vibrating screen separator having a generally planar sifting screen that is forcibly vibrated. The separator may be configured with stacked decks and serially connected sections involving multiple sifting planes. In the latter patent reference, the emphasis was upon a means of tuning the interconnecting vibratory apparatus for maximum sifting effects by optimizing vibrational energy control. In the separator sheets, cloth is tensioned between subframe sides by mounting rails that are tightened by eye nuts externally accessible at the sides of the frame. Material gravitationally flows over the vibrating screens towards a discharge position. The screen cloth is shaken by an elongated, center strip that is oscillated by a vibrator drive system.
Vibrating screen separators are subject to continuous wear and tear during operation. The screen sections must be mounted tightly in proper alignment. Screen tension is controlled by the multiple peripheral eye nuts or mounting hardware that surrounds the subframe. Adjustments are required periodically, and during routine maintenance or the replacement of screen sheets, the multiple eye nuts must be tediously inspected and adjusted to insure proper operational tension. No simple means for simply and quickly measuring screen tension has hitherto been available.
A system for easily maintaining proper screen tension with a minimum of operator effort is desirable. An adequate screen tensioning system should be quickly and easily adjustable, and means must be provided enabling an operator to quickly discern the setting of the tensioning hardware. A screen separator having tensioning elements whose settings can be readily determined visually, for example, would significantly ease the maintenance and operation burdens imposed upon the machine operators.